FAIR VALUE MEASUREMENTS (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents	$ 106,877	$ 137,394	$ 184,794
Accumulated gross unrealized gain, before tax	121	154
Accumulated gross unrealized loss, before tax	(2)	(341)
Cash, cash equivalents and debt securities available-for-sale, amortized cost	167,932	206,139
Cash, cash equivalents and debt securities available-for-sale	168,051	205,952
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Accumulated gross unrealized gain, before tax	42	116
Accumulated gross unrealized loss, before tax	0	0
Cash, cash equivalents and debt securities available-for-sale, amortized cost	118,069	148,366
Cash, cash equivalents and debt securities available-for-sale	118,111	148,482
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized cost	49,863	57,773
Accumulated gross unrealized gain, before tax	79	38
Accumulated gross unrealized loss, before tax	(2)	(341)
Debt securities, available-for-sale	49,940	57,470
Cash
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents	40,656	31,378
Cash and cash equivalents, fair value	40,656	31,378
Money market funds | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents	71,232	110,796
Cash and cash equivalents, fair value	71,232	110,796
Treasury securities | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized cost	6,181	6,192
Accumulated gross unrealized gain, before tax	42	116
Accumulated gross unrealized loss, before tax	0	0
Debt securities, available-for-sale	6,223	6,308
Certificate of deposit | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents	8,641	8,641
Cash and cash equivalents, fair value	8,641	8,641
Commercial paper | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized cost	16,194	14,979
Accumulated gross unrealized gain, before tax	0	6
Accumulated gross unrealized loss, before tax	(1)	0
Debt securities, available-for-sale	16,193	14,985
Corporate debt | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized cost	25,028	34,153
Accumulated gross unrealized gain, before tax	79	32
Accumulated gross unrealized loss, before tax	(1)	(341)
Debt securities, available-for-sale	25,106	33,844
Cash and Cash Equivalents
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash, cash equivalents and debt securities available-for-sale	106,877	137,394
Cash and Cash Equivalents | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash, cash equivalents and debt securities available-for-sale	104,971	131,798
Cash and Cash Equivalents | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale	1,906	5,596
Cash and Cash Equivalents | Cash
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents	33,739	21,002
Cash and Cash Equivalents | Money market funds | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents	71,232	110,796
Cash and Cash Equivalents | Commercial paper | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale	1,300	5,596
Cash and Cash Equivalents | Corporate debt | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale	606
Restricted Cash (Current & Non-Current)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash, cash equivalents and debt securities available-for-sale	15,558	19,017
Restricted Cash (Current & Non-Current) | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash, cash equivalents and debt securities available-for-sale	6,917	10,376
Restricted Cash (Current & Non-Current) | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale	8,641	8,641
Restricted Cash (Current & Non-Current) | Cash
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents	6,917	10,376
Restricted Cash (Current & Non-Current) | Certificate of deposit | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents	8,641	8,641
Short-Term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash, cash equivalents and debt securities available-for-sale	41,738	33,458
Short-Term Investments | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale	6,223
Short-Term Investments | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale	35,515	33,458
Short-Term Investments | Treasury securities | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale	6,223
Short-Term Investments | Commercial paper | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale	14,893	9,389
Short-Term Investments | Corporate debt | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale	20,622	24,069
Long-Term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash, cash equivalents and debt securities available-for-sale	3,878	16,083
Long-Term Investments | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale	0	6,308
Long-Term Investments | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale	3,878	9,775
Long-Term Investments | Treasury securities | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale	0	6,308
Long-Term Investments | Certificate of deposit | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale	0
Long-Term Investments | Corporate debt | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale	$ 3,878	$ 9,775